As the demand of users for bandwidth is rapidly increasing, optical transmission systems, where subscriber traffic is transmitted using optical networks, are installed to serve this demand. These networks are typically referred to as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), fiber-to-the-premise (FTTP), or fiber-to-the-home (FTTH). Each such network provides access from a central office (CO) to a building, or a home, via optical fibers installed near or up to the subscribers' locations. As the transmission quantity of such an optical cable is much greater than the bandwidth actually required by each subscriber, a passive optical network (PON) shared between a plurality of subscribers through a splitter was developed.
A diagram of a typical PON 100 is schematically shown in FIG. 1. The PON 100 includes M optical network units (ONUs) 120-1, 120-2, through 120-M, coupled to an optical line terminal (OLT) 130 via a passive optical splitter 140. To the extent that reference is made to the ONUs without regard to a specific one thereof, such ONUs will be referenced as 120. Traffic data transmission may be achieved, for example, by using asynchronous transfer mode (ATM) cells over two optical wavelengths, one for the downstream direction and another for the upstream direction. In downstream transmission, the OLT 130 receives data from a backbone network 160 and distributes the data into each ONU 120 through the splitter 140. For this purpose, the OLT 130 performs a switching function on medium access control (MAC) address of at least layer 2. Each ONU 120 filters its respective data according to, for example, a pre-assigned unique value. The ONUs 120 transmit respective data to the OLT 130 during different time slots allocated by the OLT 130 for each ONU 120. The splitter 140 splits a single line into multiple lines, for example 1 to 32.
FIG. 2 shows a schematic block diagram of the OLT 130 that includes an optical transceiver 210 and an OLT controller 220. The optical transceiver 210 acts to transmit and receive optical signals to and from the ONUs 120 via the optical splitter 140. The OLT controller 220 acts to process signals received from ONUs 120 and the backbone network 160. Specifically, the controller 220 includes an Ethernet switch 230 and a PON MAC adapter 240. The Ethernet switch 230 merely provides an interface to the backbone network 160. Ethernet packets received at the Ethernet switch 230 are sent to the PON MAC controller 240, which in turn processes the frames to generate PON frames. Abstractly, the PON MAC adapter 240 adapts between the Ethernet domain and the PON domain. That is, the PON MAC adapter 240 constructs PON frames from the Ethernet packets. Each PON frame includes a unique value (e.g., a port ID) which designates the destination ONU.
Currently, the mapping between Ethernet addresses and port-IDs as performed by conventional OLTs is based on virtual local area network (VLAN) tags included in Ethernet packets and not on MAC destination addresses of the packets. This limits the functionality of the Ethernet switch 230 as conventional switches are capable of supporting MAC address learning and providing enhanced traffic management features based on the learnt addresses. One technique to map between Ethernet MAC and port-ID using VLAN includes adding a dedicated logic circuit (e.g., FPGA) to the OLT controller 220. This increases the complexity and the cost of OLT controllers. Another technique for enabling the mapping between Ethernet and PON addresses includes manually configuring the Ethernet switch 230 with rules that define the routing information. Specifically, the rules are configured to mapping an Ethernet address to a port-ID and inserting the port-ID value in a VLAN tag.
However, the number of rules is bounded and cannot cover the entire PON address space. In addition, adding a VLAN tag by the Ethernet switch 230 prevents a VLAN manipulation by the Ethernet switch. This is a major drawback as in many cases a downstream packet has to be transmitted towards the PON with a VLAN value different than the received VLAN value.
It would be therefore advantageous to provide an efficient solution for mapping addresses between Ethernet domain and PON domain by OLT controllers.